PAPER INSTRUCTIONS:

GG282 Geomorphology and Soils

GG282 Laboratory Exercise Two, Part One
Physical Properties of Soils and Surficial Materials

This lab is to be completed and submitted before your lab next week.
Submit to YOUR lab section’s DropBox!

Introduction

Over the two weeks of lab exercise two we will examine several physical properties of soil and sediment samples.  In the first week we will:

  1. demonstrate a procedure that can be used to measure the moisture content of a soil or sediment sample,
  2. describe the property of consistency and examine how fine grained materials change with differing moisture contents, and
  3. describe how we can determine the organic content of a soil or sediment sample. 

In the second portion of lab exercise two we will:  

  • outline a method to describe soil colour,
  • illustrate how the pH of a soil can be measured,
  • demonstrate a method that can be used to determine the proportions of silt and clay in a sample

The following handout describes the methods that would have been used in the first portion of Lab Exercise Two. 

Measuring the Moisture Content of a Soil or Sediment Sample by the Gravimetric Method

The soil moisture content of a soil or sediment sample is most commonly expressed as a ratio, expressed as a percentage, of the mass (weight) of water in a given sample relative to the mass (weight) of the dry soil.  The moisture content is determined by weighing the moist soil sample, drying out the sample to a standard temperature, and then weighing the mass (weight) of the dry soil.  The water mass (or weight) is the difference between the weights of the wet and dry samples. To dry a soil sample, the oven temperature used is 105oC, and the time period at least 24 hours.  At this temperature all of the capillary water and most of the structural water will normally be evaporated from the sample. 

 

Materials

  • Drying Oven at 105oC
  • Electronic balance with a precision of ±0.001 g.
  • Aluminum weigh tins or equivalent container
  • Soil or sediment samples collected in the field with auger or similar tools Procedure
     
    Figure 1:     Drying Oven and Electronic Balance in 3C2, Arts Building.
  • Label each aluminum tin with a unique identifier, each tin should be clean and dry. Ideally the tins would have been oven dried and stored in a desiccator prior to use.
  • Weigh each aluminum tin, and record this weight (“tin weight”)
  • Place a small representative sample of the soil or sample into the tin, use approximately 5 to 10 g and record this weight as the “wet soil + tin weight”. 
  • Place the sample in the oven 105oC, and dry for 24 hours.
  • Remove the sample from the oven and place in a desiccator to cool.
  • Once cooled, weigh the dry sample, and record this weight as weight of “dry soil + tin weight”.
  • As a check on your method you may choose to multiple samples and repeat the drying and weighing to ensure consistent results in the dry weight.

For each sample you would have a “tin weight”, “wet soil + tin weight”, and “dry soil + tin weight”.  You will be given data to use.

Calculations

To express the moisture content of a soil as a percentage, we need to know the weight of soil moisture and the weight of the dry soil.

Calculate the dry soil weight by subtracting the “tin weight” from the “dry soil + tin weight”

Calculate the moisture weight by subtracting the  “dry soil + tin weight” from the “wet soil + tin weight”

Then determine the moisture content from:

Moisture Content (%) = {(moisture weight)/(dry soil weight)}*100

Soil Consistency

The term consistency is used to denote the ease with which a soil may be deformed under pressure.  A glossary of soil terms is found at:  https://www.soils.org/publications/soils-glossary. For soil samples there are a variety of terms that can be used for consistency (see for example https://www.soils.org/files/publications/soils-glossary/table-1.pdf).  Soil consistency is related to cohesion and adhesion in a sample (adhesion refers to the attraction of water molecules to the surface of a soil particle, also called adsorption).

In this lab we will examine one way to describe the consistency of fine grained soils (samples). Fine grained soils may have a high consistency when dry (e.g. extremely hard) but have a much lower consistency when moist.  

In the early 20th century a Swedish soil scientist, Albert Atterberg, examined the physical properties of fine grained soils focusing on consistency or consistence.  Atterberg defined seven “limits of consistency” to denote changes that occur as the moisture content of the soil is altered.

These limits may also be used to classify fine grained soils (e.g. the Unified Soil Classification System uses Atterberg limits for fine grained soils).  In current practice, only two of the Atterberg limits are commonly measured: the Liquid and Plastic Limits.  The plastic limit is the moisture content in a fine grained soil that denotes a change in soil consistency from a semi-solid state to a plastic (flexible) state. The liquid limit is the moisture content in a fine grained soil that denotes a change in soil consistency from a plastic state to a viscous fluid state.  A third limit called the shrinkage limit is also used occasionally, it is the moisture content that denotes when the soil volume will not be further reduced if the moisture content is reduced. Most fine grained soils contract (shrink) as their moisture content falls.  Another parameter that is used in soil science is called the Plasticity Index or Plasticity Number, this index is the numerical difference between the Plastic and Liquid limits.

Atterberg limits also give us some insight into the mechanical properties of soils.  Note that in the context of Atterberg limits, the term ‘soil’ applies to any unconsolidated material (i.e. not bedrock).  Some fine grained soils may behave as a plastic material at relatively low moisture contents, when the moisture content in a fine grained soil rises to the liquid limit the materials may deform as a mass flow.

There are many instances when we may need to measure the moisture content of a soil, the method described below is useful for a range of circumstances.

Equipment

Drying Oven, Balance, Moisture Tin (Can), Gloves, Spatula

Procedure

For measuring the moisture content of a sample we follow the same procedure outlined above.  The steps are summarized below.

  1. Take a clean dry moisture tin, label and record the number on the tin. Weigh the empty dry can on the balance (tin weight).
  2. Place a small amount of the moist soil or sediment sample in the moisture tin.  Weigh the tin and moist soil or sediment sample on the balance.  Record the weight (wet soil and tin).
  3. Place the moisture tin containing the moist sample into the drying oven.  The temperature in the oven should be set to 105 °C.  Leave the sample in the oven for at least 24 hours.
  4. Remove the moisture tin from the oven.  Allow the tin to cool to room temperature (may place in a desiccator).  Once cool, weigh the moisture tin, and dry soil sample on the balance, record the weight (tin and dry soil).
  5. Empty the moisture tin and clean the tin.  Repeat the procedure for a quality check.

Calculation

  1. Determine the weight of the dry soil.

Weight of Dry Soil = (Weight of Tin and Dry Soil) - (Weight of Tin)

  • Determine the weight of the moisture.

Moisture Weight = (Weight of Tin and Moist Soil) -  (Weight of Tin and Dry Soil)

  • Determine the moisture content.

Moisture content (%) = {(Moisture Weight)/(Weight of Dry Soil)}*100

Atterberg Limits

The Atterberg limits may be measured using a Casagrande apparatus or a Cone Penetrometer.  In the lab we will use the Casagrande Method.

Equipment

Casagrande Device (liquid limit device), Evaporating Dish, Grooving Tool with Gauge,

Moisture Tins, Balance, Glass plate, Spatula, Wash bottle with Distilled Water, Drying Oven (at 105°C)

Figure 2: Equipment needed for determination of liquid limit.  The Casagrande device is the open cup.  A sample of moist soil is placed in the cup and subjected to stress (described below).

Liquid Limit Procedure  (https://www.youtube.com/watch?app=desktop&v=GxXqqIuCfT0)

  1. Acquire the soil samples, sieve the samples through a #40 standard sieve (0.42 mm). Materials that pass through this sieve are medium sands and below. Discard any materials that are coarser than medium sand.  The sample should be dry and disaggregated (pulverized).
  2. The sample mass should be approximately 100 to 125 grams.  Place the sample into a porcelain dish.  Mix the sample with a small amount of distilled water until the sample has the appearance of a smooth uniformly coloured paste.  The soil and water should be well mixed.  Cover the dish.
  3. Weigh three empty moisture tins with their lids, record the weight data and the tin number and their lids.
  4. If necessary, adjust the Casagrande apparatus so that the height of the drop of the cup is equal to 1 cm.  This distance can be checked by using the calibration block at the end of the grooving tool.  Make the adjustment with respect to the position of the worn spot on the base of the cup.  Practice turning the crank at a rate of two drops per second.
  5. Place a portion of the previously mixed soil into the cup of the Casagrande apparatus centred at the point where the cup rests on the base (the cup can be removed from the apparatus at this point but attempt to fill the cup in place).  Gently squeeze the moist soil down to drive out air pockets.  The sample should be approximately 10 mm deep in the central portion and the sample should be patted to a horizontal surface (see Figure 2).
  6. Using the grooving tool cut a clean straight groove down the center of the sample.  Hold the tool perpendicular to the surface as the cut is made (Figure 3).  During the cut, the soil sample should not slide on the cup surface.

Figure 3: The soil sample in place with a clean cut (left), the sample closes as it is agitated (right).

  • Wipe the underside of the cup and the top surface of the base to ensure there is no soil between the cup and base. 
  • Turn the crank of the apparatus at a rate of approximately two drops per second.  Count the number of drops.  As the sample is agitated, the grove will begin to close (usually in the deepest part of the sample), when the grove has closed over a distance of 13 mm (some use 12 mm or half an inch) stop rotating the crank (see Figure 2). 
  • Record the number of drops that were required to close the grove over a distance of 13 mm.  Ideally that number will be in a range between 15 and 35 drops.  If the number of drops is greater than 50 or less than 15, remove the sample and re-mix the sample to a moisture content that will produce a number of drops closer to 25.
  • Using the spatula, remove a portion of the sample from the area in the cup where the grove was closed.  Draw the spatula from one side of the sample to the other side.  Place that sample in a pre-weighted dry and labelled moisture tin.
  • Weigh the moist sample and the moisture tin on the balance, record the weight.
  • Repeat steps 5 through 11 at least two more times. With each successive trial mix the soil and moisture well.
  • For each moist sample, place them in the oven at 105oC and allow to dry for at least 24 hours.
  • Recover the dry sample from the oven, weigh the moisture tin and sample on the balance, record the weight.
  • Calculate the moisture content of the sample.

The objective is to have at least three determinations for the soil sample.  The data required to determine the liquid limit are the moisture contents of the sample and the number of blows required to close the grove 13 mm.  At the beginning of the next lab we will pool the data and discuss the calculations.

•      Plastic Limit Procedure (https://www.youtube.com/watch?v=fUjiDMBEUi4)

  1. Weigh a dry empty moisture tin and lid and record the weight.
  2. Take approximately 20 grams of sample and mix well with distilled water to a consistency that will allow you to form a ribbon without sticking to your hand.
  3. Form the moistened soil sample into an ellipsoidal mass. Roll the sample between your palm and a glass plate or the table top.  Produce a ribbon with a uniform diameter approximately equal to one eighth of an inch (3.2 mm).
  4. When the ribbon reaches the correct diameter, break the thread into several pieces. Knead and reform the pieces into an ellipsoidal mass and re-roll it.  Continue this alternate rolling, gathering together, kneading and re-rolling until the thread crumbles under the pressure required for rolling and can no longer be rolled into a 3.2 mm diameter thread.

Figure 4: Rolling a 3.2 mm thread to determine the plastic limit.

  • Gather the portions of the fractured and crumbled ribbon together and place the sample into a dry pre-weighed moisture tin.
  • Weigh the moisture tin and moist sample on the balance, record the weight.
  • Place the sample in the oven at 105oC for a least 24 hours.
  • Remove the moisture tin and dry sample from the oven, allow to cool to room temperature, and weigh the tin and dry sample.  Record the weight.
  • Calculate the moisture content of the sample.

Ideally, the plastic limit would be measured for a single sample at least three times (three trials).  Your TA will give you direction on the number of samples we will do.

Determination of Soil Organic Matter by Loss on Ignition (LOI)
https://www.youtube.com/watch?v=87Ilsj3QOwE                       

The organic content of soils have a significant impact on the fertility, moisture content, structure and consistency of soils.  Variations in organic content are used in the classification of soils. There are several techniques that can be used to determine the organic content of a soil or sediment sample.  One simple technique involves heating the sample to a very high temperature to oxidize the organic material.  Once oxidized the organic material is combusted into carbon dioxide and lost from the sample.  This technique is called Loss on Ignition (LOI). 

In this method a small sample of oven dry soil is introduced into a high temperature furnace.  The soil sample should be dried at 105oC for at least 24 hours prior to ignition in the furnace.  A small clean, dry and pre-weighed porcelain cup is used to hold the soil sample.  The temperature of the furnace used to oxidize the organic carbon should be in the range 375oC to 550oC.  There is no universal agreement in the literature about the ideal ignition temperature.  If the temperature of the furnace is set too high, mineral material in the soil will also become oxidized and the weight loss will be excessive, which will result in an inflated estimate of the organic content.  In comparing the results from the LOI technique with other methods, good results occur when the ignition temperature is relatively low (e.g. 375 to 390oC range) and the combustion time is long (24 hours).  The sample should be introduced into the furnace and the temperature brought up to a maximum slowly. 

By recording the sample weight prior to combustion, and after the combustion, it is possible to determine the weight of the organic material lost.  The organic matter content is then expressed as a percentage, by determining the ratio between the weight of organic material combusted and the weight of the original dry sample.

Materials

  • small ceramic crucibles
  • high temperature oven (muffle furnace)
  • sub-samples of each soil (approximately 5-10 grams)
  • thermal gloves and long handled tongs

Figure 5: Muffle furnace, crucibles, gloves in 3C2, Arts Bulding.

Procedure

  1. Prepare the soil sample by drying in oven at 105oC for 24 hours.
  2. Label and weigh the crucibles.  Prepare each crucible (ceramic cup) by cleaning and drying (in oven), record the weight of clean and dry crucibles (ideally the crucible would be kept in a desiccating chamber to prevent it from absorbing moisture from the air) after it is weighed. Record the crucible weight (this is the ‘tare’ weight).
  3. Add the oven dried soil sample to the crucible(s) (~7-10 grams). Weigh and record the weight of the crucible plus dry sample.  Make sure you record which soil sample is in each labeled crucible.  This is the pre-combustion weight (pre-ignition weight).
  4. Turn on high temperature oven (muffle furnace) and set the temperature to 390 degrees.  The oven should be programed to increase its temperature slowly, about 5 oC/min.
  5. Using the metal tongs carefully place the crucible(s) into the furnace and shut the door.
  6. For complete combustion, the sample should be allowed to rest in the furnace for 24 hours.
  7. Following combustion, turn off the oven, and open the oven door.  Allow the system to cool for 20 minutes.
  8. Put on the thermal gloves and use the metal tongs to carefully remove the crucibles and place them on something that will not burn (i.e. piece of glass) DO NOT PUT HOT CRUCIBLES ON THE LAB BENCH.  Allow the samples to completely cool.
  • Once cool, weigh the crucible and combusted sample, record this weight as the crucible plus combusted sample.  This is the post combustion weight (post ignition weight).

Calculations

To determine the weight of the organic matter that were lost on ignition (LOI), subtract the post combustion weight from the pre combustion weight.  Then use the following relation to calculate the percent organic matter content of the soil samples:

Percentage of Organic Matter = {(weight of organic matter)/(pre combustion weight)}*100

Do you have a similar assignment and would want someone to complete it for you? Click on the ORDER NOW option to get instant services at essayloop.com